readSTL: Read and write STL (stereolithography) format files

Description

These functions read and write STL files. This is a simple file format that
is commonly used in 3D printing. It does not represent text,
only triangles. The writeSTL function converts some RGL object
types to triangles.

A connection or filename.

ascii

Whether to use the ASCII format or the binary format.

plot

On reading, should the object be plotted?

...

If plotting, other parameters to pass to triangles3d

pointRadius, lineRadius

The radius of points and lines relative to the overall scale of the figure.

pointShape

A mesh shape to use for points. It is scaled by the pointRadius.

lineSides

Lines are rendered as cylinders with this many sides.

ids

The identifiers (from rgl.ids) of the
objects to write. If NULL, try to write everything.

Details

The current implementation is limited. For reading, it ignores normals
and color information. For writing, it only outputs triangles, quads, planes, spheres,
points, line segments, line strips and surfaces, and does not write color information.
Lines and points are rendered in an isometric scale: if your data scales vary, they
will look strange.

Since the STL format only allows one object per file, all RGL objects
are combined into a single object when output.

The output file is readable by Blender and Meshlab; the latter can write in
a number of other formats, including U3D, suitable for import into a PDF document.

Value

readSTL invisibly returns the object id if plot = TRUE, or (visibly)
a matrix of vertices of the triangles if not.

writeSTL invisibly returns the name of the connection to which the
data was written.

Author(s)

Duncan Murdoch

References

The file format was found on Wikipedia on October 25, 2012. I learned
about the STL file format from David Smith's blog reporting on
Ian Walker's r2stl function.